In recent years, there is a growing concern about an influence of an atmospheric environment on health, and for example, a new environmental standard for an atmospheric microparticle concentration has been established. For example, diesel microparticles are deposited in the back of the airway such as the alveoli to harm health. A particle size of microparticles is an important factor for a health risk. As the particle size is smaller, there is a higher risk that the particles reach the alveoli through the mouth, nose, trachea, and bronchi that are organs of respiration of a human to harm health. Thus, a standard based on an atmospheric concentration of particles (PM2.5) having an aerodynamic diameter of 2.5 μm or the like is also known. Further, in a special environment in which higher cleanliness of an atmospheric environment is required, such as a clean room, a production environment, or a medical environment, there is a demand for a method of measuring an atmospheric microparticle concentration with higher sensitivity.
In order to avoid a health influence risk and reduce a risk of deterioration in quality of products and services using a special atmospheric environment such as a clean room, a production environment, or a medical environment, it is important to monitor the status of a concentration of contamination with atmospheric microparticles. Further, it is important to obtain information on a mass concentration of each chemical composition of atmospheric microparticles, in order to identify a source of contamination to improve an atmospheric environment.
Conventionally, as a method of measuring a chemical composition of atmospheric microparticles, a filter collection and offline chemical analysis method has been widely used. This method involves sucking air to collect microparticles on a filter, transferring the microparticles to an analysis chamber or the like, followed by solution extraction, heat treatment, or the like, and chemically analyzing the microparticles. However, according to this method, it takes a collection time of about several hours to several days for analyzing an average atmospheric environment concentration level. A highly volatile component may be evaporated while being collected and transferred, and a gas phase component may adsorb to serve as an interfering factor during the collection of the microparticles. Thus, the above-mentioned method has a problem in terms of quantitativity. Further, the method is performed by offline analysis, and hence, it requires a great amount of labor for obtaining data continuously for a long period of time.
Accordingly, there is a demand for the development of a method for online measurement of a chemical composition, characteristics, and the like of atmospheric microparticles. As an apparatus and method applicable to such online measurement, for example, Patent Literature 1 below describes a method involving introducing particles into a high-vacuum chamber, irradiating flying particles with a laser to ionize a constituent component thereof, and analyzing a mass of the ionized component. Further, Patent Literature 2 and Non Patent Literatures 1 and 2 below describe a method involving introducing a particle beam generated by a particle beam generator (aerodynamic lens) for generating a particle beam of microparticles in a gas into a high-vacuum chamber, causing the particles to collide with a heated copper substrate with a molybdenum foil formed on the surface, heated tungsten, or the like to heat and gasify the particles, ionizing the resultant particles, and analyzing a mass of the particles.